Anodic protection for plating system



@ci 17, 1967 w. l. CLARK ETAL $341768 ANODIC PROTECTION FOR PLATINOSYSTEM Filed Jan. 29, 1965 2 Sheets-Sheet l BRucEGRIGGS DARRELL'D. HAYSGem/AINE E JACKY BY /-k-u( Q2 ATTORNE V Oct 17, 1967 w. l. CLARK ETALNODIC PROTECTION FOR PLATING SYSTEM Filed Jan, 29, 1955 K12, ff; 21,.0.1 26

INvENTaRs.

WESLE Y I. CLA/2K Bleues GRIGGS DARRELLD. HAY; GERMAIN; E JACKY fdr 32Illu.

United States This invention relates to a continuously regeneratedplating system in which nickel is deposited by the electroless system.More specifically, the invention relates to the electrolytic passivationof certain surfaces in the system.

In systems of the above type, stainless steel, rather than nonmetallicmaterials, has been employed for the containment equipment, because ofits superiority in heat transfer. The disadvantage is that thestainless-steel surfaces must frequently be treated with warm nitricacid, which forms and maintains a surface lm that is not catalytic tothe plating reaction. Nitric-acid passivation of stainless steel iseffective in preventing an unwanted plating reaction, but is lbothtime-consuming and expensive, because it must be applied often.

It is known to carry out continuous electroyltic passivation of astainless steel tank in a batch system for the electroless plating ofnickel.

We have discovered that electrolytic passivation of stainless-steelsurfaces may be employed in a complete, continuously regenerated systemfor the electroless plating of nickel.

In the drawings:

FIG. 1 is a diagrammatic View of the novel system of the presentinvention;

FIG. 2 is a fragmentary sectional view showing the use of a cathodeplate between sections of pipe in the system; and

FIG. 3 is an elevational view of the cathode plate.

As shown in FIG. 1, a plating tank contains a plating solution, which isheated by a steam coil 11. The bottom of the plating tank 10 isconnected by a pipe 12 with an upper portion of a cooler regeneratortank 13. The solution in the tank 13 is cooled by a coolingwater coil14. An agitator 14a extends into the solution in tank 13. A pipe 15extends from the bottom of the cooler regenerator tank 13 to a heatexchanger 16, by way of a pH electrode Well 17, a pump 18, a iilter 19,and an automatic-ilow-control valve 2i) A by-pass pipe 21, controlled bya valve 22, connects the pipe 12 and the ppoe 15 ahead of the pHelectrode well 17.

At the heat exchanger 16, which is operated by steam entering through aninlet 23 and leaving through an outlet 24, the pipe 15 is connected withone end of a coil 25 located in the heat exchanger. The other end of thecoil 25 is connected with a pipe 26, which extends through the top ofthe plating tank 10 near the bottom thereof.

The above described system is operated by placing a plating solutioncontaining a water-soluble nickel salt, a hypophosphite, and a bufferingagent in plating tank 10 and heating the solution with steam in heatingcoil 11. The article to be plated, for example, an aluminumjacketednuclear-fuel element, is dipped into the solution for a suitable time toobtain a thin, adherent, corrosionresistant coating of nickel thereon.The plating solution is continuously regenerated by circulating thesolution from plating tank 10 through cooler regenerator tank 13 wheremake-up chemicals are added, and filter 19 to heat exchanger 16, andthen to plating tank 10. The process thus described is conventional inthe alt. As

and opens into a region.

atent 0 to 42 are located in the 3,347,?68 Patented Get. l?, 1967 hasbeen pointed out a problem arises, because the solution plates out onthe tanks and pipes and this problem has not been completely overcome inaccordance with the prior art practice of passivating the metal withnitricacid wash.

According to the present invention, however, this problem has beencompletely overcome by immersing a stainless-steel sheet 27 in thesolution in plating tank 10 and inserting a plurality of stainless-steelring inserts 28 into the pipes 12, 21, 15, and 26 while insulating theinserts from the pipes and making the said metal sheet 27 and ringinserts 28 cathodic with respect to the tanks 11 and 13 and pipes. Thisis accomplished by connecting the sheet 27 and the ring inserts 28 tothe negative side of a 12-volt `battery 28a, and the pipes 12, 21, 15,and 26, and tanks 10 and 13 to the positive side of said battery.

As shown in FIG. 2, each of pipes 12, 21, 15 and 26 which are ofstainless steel, is formed of sections 29 having outwardly extendingilanges 30. Between each pair of adjacent flanges 30, one of the ringinserts 28 is clamped and is insulated therefrom by a pair of Teflonrings 31. The flanges 30 are secured to one another by bolts 32 and nuts33. The bolts electrically connect the pipe sections 30. The innerdiameter of the ring insert 28 is greater than that of the Teilon rings31 and that of the pipe sections 29. The inner diameter of the Teonrings 31 is greater than that of the pipe sections 29. The outerdiameter of the flanges 30 is greater than that of the Tellon rings 31and that of the ring inselt 28, except for a tail 34 so that the bolts32 extending through the ilanges 30 clear the Teon rings 31 and the ringinsert 28. The outer diameter of the ring insert 28, except for the tail34 which is attached to an electrical connector 35 leading to thebattery 28a, is less than the outer diameter of the Teon rings 31. Thering inserts 28 are located at some seven regions of the pipes 12, 21,15, and 26, identified as regions 36, 37, 38, 39, 40, 41, and 42. Region36 is in pipe 12 just below plating tank 10. Region 37 is in pipe 12adjacent its connection with by-pass pipe 21. Region 38 is in pipe 21adjacent its connection with pipe 12. Region 39 is in pipe 12 adjacentthe cooler regenerator tank 13. Region 40 is in pipe 15 adjacent theheat exchanger 16. Region 41 is in pipe 26 adjacent the heat exchanger16. Region 42 is in pipe 26 adjacent the plating tank 10. All theseregions 36 plating solution where the temperature of the solution isabove 60 C. and therefore is likely to plate out on the 'tanks 10 and 13and pipes 12, 21, 15, and 26. This is in contrast with the platingsolution throughout the length of pipe 15 and associated parts, where,except adjacent the heat exchanger 16, the plating solution is at atemperature of 60 C. or 'below and therefore is not likely to plate out.

Any plating action thereby occurs on the said metal plate 27 or ringinserts and not on the surface of the tank 11 and 13 or pipes 12, 21,15, and 26. The plate 27 can be removed and replaced while the ringinserts need not be removed, since any nickel thereon is removed whenthe system is periodically cleaned by flushing the system with nitricacid. The following speciic example illustrates application of thepresent invention.

Example A plating solution which is 0.10 molar in nickel sulfate, 0.3molar in sodium hypophosphite, and 0.3 molar in lactic acid having a pHof 4.40 to 4.45 was employed and plating was carried out at atemperature determined by plate deposition rate which was maintained at0.5 mil/hr. Bath operating temperatures ranged from C. on a new bath to93 C. on an aged bath. The plating solution is continuously circulatedthrough the system at a rate of 4 gallons per minute. It is first pumpedto cooler t a .a regenerator tank 13 where the solution is cooled to atemperature of 60 C. and the chemicals utilized in the nickel-platingreactions are replenished. 2M nickel sulfate, 6M sodium hypophosphite,and 8M sodium hydroxide to control pH are employed. No additions oflactic acid are necessary. From the tank 13 the plating bath is pumpedthrough filter 19, coil 25 in heat exchanger i6, where the temperatureof the solution is increased to plating bath temperature, and back intothe plating tank 10.

The pH of the circulating bath is continuously measured with electrodesin pH electrode Well 1.7. The output signal from a pH recorder operatesa metering pump which proportions the three chemical addition streamsinto the regenerating tank.

A current of 40 ma./ft.2 was found to be suficient to prevent thedeposition of nickel on the stainless steel tank and pipes. Inspectionshows no deposit of nickel on the stainless steel pipes and tanks but aheavy coat of nickel on the ring inserts and stainless plate.

In a preliminary experiment the electrolytic protection was disconnectedand the solution heated to 95 C. A large amount of foam formed afterabout l hour at temperature. Inspections of the system showed thatnickel had plated out on the interior of the tanks and pipes. It is thusevident that the electrolytic protecting system is necessary to theoperation ofthe system.

It is understood that the invention is not to be limited by the detailsgiven herein but that it may be modified within the scope of theappended claims.

The embodiments ofthe invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a continuously regenerated system for depositing nickel plate bychemical reduction in an aqueous solution, comprising a metal platingtank, a cooler regenerator tank, a heat exchanger, and metal pipes forconveying the solution from the plating tank to the cooler regeneratortank, from the cooler regenerator tank to the heat exchanger, and fromthe heat exchanger to the plating tank; the combination therewith, of ametal sheet irnmersed in the plating tank, a plurality of metal ringinserts applied to the pipes so as to be insulated therefrom, twoinserts being applied adjacent to the inlet and outlet of the platingtank, another insert ybeing applied adjacent the inlet to the coolerregenerator tank, still another insert being applied between thelast-mentioned insert and the insert adjacent the outlet of the platingtank, two inserts being applied adjacent the inlet and outlet of theheat exchanger, means for connecting the negative side of adirect-current source to the metal sheet and to the ring inserts, andmeans for connecting the positive side of the direct-current source tothe pipes and thereby also to the metal plating tank.

2. In the system as specified in claim 1, the pipes being formed ofsections having outwardly extending flanges at their adjacent ends, eachof the ring inserts being located between a pair of adjacent flanges, apair of insulating rings applied on opposite sides of the ring insertbetween the same and the flanges, the inner diameter of each ring insertbeing greater than the inner diameter of the associated pipe sections,the outer diameter of each ring insert being less than the outerdiameter of the associated flanges on the pipe sections, the saidflanges being attached and electrically connected to one another bybolts located radially outward of the associated ring insert.

3. In the system as specified in claim 2, the pipes and ring insertsbeing formed of stainless steel.

4. In a continuously regenerated system for depositing nickel plate bychemical 4reduction in an aqueous solution, comprising a metal platingtank, a cooler regenerator tank, a heat exchanger, a first metal pipefor conveying the solution from the plating tank to the coolerregenerator tank, a second metal pipe for conveying the solution fromthe cooler regenerator tank to the heat exchanger, a third metal pipefor conveying the solution from the heat exchanger to the plating tank,and a metal by-pass pipe connecting the first and second pipes; thecombination therewith, of a metal sheet immersed in the plating tank, aplurality of metal ring inserts applied to the pipes so as to `beinsulated therefrom, two inserts being applied to the third and firstpipes adjacent to the inlet and Outlet of the plating tank, anotherinsert being applied to the first pipe adjacent the inlet to the coolerregenerator tank, still another insert being applied to the first pipeadjacent its connection with the by-pass pipe, still an- `other insertbeing applied to the by-pass pipe adjacent its connection with the firstpipe, two more inserts being applied to the second and third pipesadjacent the inlet and outlet of the heat exchanger, means or connectingthe negative side of a direct-current source to the metal sheet and tothe ring inserts, and means for connecting the positive side of thedirect-current source to the pipes and thereby also to the metal platingtank.

5. In the system as specified in claim 4, the pipes being formed ofsections having outwardly extending flanges at their adjacent ends, eachof the ring inserts Ibeing located between a pair of adjacent flanges, apair of insulating rings applied on opposite sides of the ring insertbetween the same and the flanges, the inner diameter of each ring insertbeing greater than the inner diameter of the associated pipe sections,the outer diameter of each ring insert being less than the outerdiameter of the associated flanges on the pipe sections, the innerdiameter of the insulating rings being less than that of the associatedring insert and greater than that of the associated pipe sections, theouter diameter of the insulating rings being greater than that of theassociated ring insert and less than that of the associated flanges onthe pipe sections, the said flanges being attached and electricallyconnected to one another by bolts located radially outward of theassociated ring insert and the insulating rings.

6. In the system as specified in claim 5, the pipes and ring insertsbeing formed of stainless steel.

References Cited UNITED STATES PATENTS 1,592,175 7/1926 Boyd 204--1961,825,477 9/1931 Reichart 204-196 2,076,422 4/ 1937 Zimmerer et al2041-196 2,193,667 3/1940 Bary 204-196 2,377,792 6/ 1945 Lawrence et al204--196 2,762,767 9/ 1956 Mosher et al 204-196 3,208,927 9/ 1965Hutchison et al. 204-147 ROBERT K. MIHALEK, Primary Examiner.

T. HUNG, Assistant Examiner.

1. IN A CONTINUOUSLY REGENERATED SYSTEM FOR DEPOSITING NICKEL PLATE BYCHEMICAL REDUCTION IN AN AQUEOUS SOLUTION, COMPRISING A METAL PLATINGTANK, A COOLER REGENERATOR TANK, A HEAT EXCHANGER, AND METAL PIPES FORCONVEYING THE SOLUTION FROM THE PLATING TANK TO THE COOLER REGENERATORTANK, FROM THE COOLER REGENERATOR TANK TO THE HEAT EXCHANGER, AND FROMTHE HEAT EXCHANGER TO THE PLATING TANK; THE COMBINATION THEREWITH, OF AMETAL SHEET IMMERSED IN THE PLATING TANK, A PLURALITY OF METAL RINGINSERTS APPLIED TO THE PIPES SO AS TO BE INSULATED THEREFROM, TWOINSERTS BEING APPLIED ADJACENT TO THE INLET AND OUTLET OF THE PLATINGTANK, ANOTHER INSERT BEING APPLIED ADJACENT THE INLET TO THE COOLERREGENERATOR TANK, STILL ANOTHER INSERT BEING APPLIED BETWEEN THELAST-MENTIONED INSERT AND THE INSERT ADJACENT THE OUTLET OF THE PLATINGTANK, TWO INSERTS BEING APPLIED ADJACENT THE INLET AND OUTLET OF THEHEAT EXCHANGER, MEANS FOR CONNECTING THE NEGATIVE SIDE OF ADIRECT-CURRENT SOURCE TO THE METAL SHEET AND TO THE RING INSERTS, ANDMEANS FOR CONNECTING THE POSITIVE SIDE OF THE DIRECT-CURRENT SOURCE TOTHE PIPES AND THEREBY ALSO TO THE METAL PLATING TANK.